Since 1981 we have been studying prostate cancer (Pca) by mass screening in three cities, eight towns and seven villages in Gunma prefecture, Japan. From 1981 to 1985, 5,770 subjects were examined. The clinical character of Pca detected by mass screening is compared with control (i.e., Pca detected in the outpatient clinic in Gunma University). Of the 54 Pca patients detected by mass screening (Stage B: 28, C: 8, D: 18), approximately 50% had early-stage Pca. The ratio of early-stage Pca is significantly higher than in the control. An extended survival rate in high-stage Pca detected by mass screening also was observed through comparison with control. We determined two types of Pca in advanced stage: (1) asymptomatic or less symptomatic and better prognostic Pca found in mass screening and (2) symptomatic and worse prognostic Pca found in control.

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